CA2434329C - Method of barge mining oil sands - Google Patents

Abstract

Oil sands are flooded and then dredge mined via barges. The mined ore and water form a slurry which is pumped to a floating plant where the slurry may be processed, or the bitumen may be extracted. The process ensures the oil sands do not freeze, making excavation easier during the winter months, and reducing slowdowns due to frost lumps. The process also eliminates the need to use shovels and trucks in the mining pits, resulting in an overall reduction in costs and a reduction in carbon dioxide emissions.

Description

METHOD OF BARGE MINING OIL SANDS
Field of the Invention This invention relates to the mining of oil sands for the purpose of extracting oil therefrom.
Background of the Invention The Athabasca oil sands consist of vast areas of sand infused with bitumen.
The bitumen is recoverable where it is present as a bitumen film on the surface of wet grains of sand. The sand is often overlain by various types of overburden such as muskeg, clay, sand, gravel, fill and lean oil sand. Limestone bedrock typically lies underneath the oil sand, but sometimes coal, mud, stone or other substance is the underlying material.
Where possible, the oil sand deposits are harvested by open-pit mining. The overburden is stripped off and used for various purposes. Muskeg is often stockpiled separately for future land reclamation, some materials are used to construct haul roads or dykes for tailing ponds, and the remaining materials are placed in waste dumps.
Following the stripping, the oil sands are excavated using shovels and delivered by diesel-powered trucks to hoppers, crushers and sizers that break down any large lumps.
The ore is then conveyed to a coarse ore stockpile, or surge. It is fed from the surge via a reclaim conveyer to a preparation plant, where it is blended with hot water, steam, caustic, and naturally entrained air, and agitated to form a slurry having a temperature of 80°C. The slurry is pumped to an extraction plant that is often several kilometres away from the excavation site. A conditioning agent comprising a flotation agent and a frother may be added to the slurry to improve recovery of bitumen. In older operations, the surge may be eliminated; the sized material is fed directly to the preparation plant via a conveyer.

At the extraction plant, bitumen is separated from the sand. The bitumen is then pumped to an upgrader for processing, while the sand and water are pumped back to tailing ponds, usually mined-out pits.
The Athabasca oil sands comprise water-wetted sand grains having viscous bitumen flecks trapped between the grains. The bitumen-infused sand lends itself to the separation or dispersion of the bitumen from the sand grains by slurrying the as-mined sand in water so that the bitumen flecks move into the aqueous phase.
For example, U.S. Patent No. 5,264,118 to Cymerman et al discloses a pipeline conditioning process for mined oil-sand wherein the oil sand slurry is pumped through a pipeline of at least 2500 metres long so that, in the course of being pumped therethrough, sufficient coalescence and aeration of bitumen occurs so that, when subsequently retained in the gravity separation vessel under quiescent conditions, a viable amount of bitumen floats, forms froth, and is recovered. More particularly, the slurry may be introduced directly into the primary separation vessel of a conventional separation circuit, wherein spontaneous flotation takes place to yield total recovery, underflow loss, and froth quality values that are comparable to those obtained by a conventional extraction train involving a tumbler and separation circuit. The slurry may be at a relatively low temperature, and yet conditioning may still be successfully completed. In addition, if the completely conditioned slurry is subjected to separation of the coarse solids (as by settling by gravity or enhanced settling, such as with cyclones) part way along its passage through the pipeline, it is found that the solids will readily separate in a substantially clean condition. The remaining slurry may then be pumped through the pipeline for the remainder of the distance to the primary separation plant.
U.S. Patent No. 4,110,195 to Hardin discloses an apparatus and process for extracting oil or bitumen from oil sands. The process is essentially an abrading and controlled separation process. The process can be operated with "cold" water that need only be heated during the winter months, may include the use of lime but does not require solvents, and may use neutral pH water so that the clay in the oil sands does not form

-2-a gel and can be removed, to a large extent, in a settling tank. It is possible to cause the bitumen to be substantially entirely separated from the sand particles (excepting fines) by a mechanism which is wholly or very largely mechanical.
The mining of oil sands and extraction of bitumen is a very costly process.
Four reasons for the high costs are the poor underfoot conditions, the extremely high abrasion factors, the need for ripping and blasting during the winter, and the blocking of the conveyances by frozen lumps of sand.
Oil sands are difficult to drive on once disturbed, since they have little shear strength and tend to become badly rutted. Trucks have trouble getting through even in good weather, and in wet weather they often become stuck. Sand and limestone are often used to strengthen frequently-travelled areas; this is not only costly, but has only limited success.
Oil sands are very abrasive, and often tightly packed. Digging can therefore be very costly, as ground-engaging tools must be frequently replaced.
During the winter, much of the oil sands are frozen, necessitating expensive ripping, drilling andlor blasting. In addition, the coarse ore piles downstream of the sizers frequently become plugged with frost lumps. The sizer must then be stopped, and the surge piles excavated. Older feed systems without surges have continual spillage of rocks and frost lumps, causing costly clean-up year-round, and especially during the winter.
For example, a typical excavation might require seven 40-cubic metre electric or diesel-powered shovels and twenty-five 300-400-tonne diesel trucks to haul 220,000 cubic metres of oil sands to the sizers. This operation, including support equipment for building haul roads, drilling and ripping frost, handling oversize ore, and crushing, requires up to some 130,000 HP or perhaps more. This works out to approximately one billion HP-hours per year.

-3-The use of heavy equipment also results in the production of significant C02 emissions.
A less costly method of mining oil sands is required.
Summary of the Invention An object of the present invention is to provide a reduced-cost method for mining oil sands.
The oil sand pits are flooded with water and mined in a series of cells with dredging barges rather than shovels and trucks. The overburden may be stripped prior to the flooding by traditional methods, or after flooding, by dredging. The low permeability of oil sand minimizes leakage and reduces the likelihood of environmental damage.
If necessary, permeable areas can be sealed with membranes, grout or even bitumen.
The barges are fitted with conventional dredging equipment, such as a cutter-head system for loosening tightly packed material. The excavation proceeds in horizontal layers at the bottom of the pond, the water level being regulated by pumping water back and forth between the mining pond and tailing ponds.
With the use of barges, the need for trucks to drive on unstable oil sands for excavation purposes is eliminated or reduced. This translates into savings in cost.
Once each cell has been mined down to the bedrock level, it is reflooded to allow the barge to navigate into the next cell and begin excavation. A number of cells may operate concurrently at various stages of completion, with one or more dredges operating in each cell. In this way, ore grade may be controlled by adjusting and blending flows from different depths, and throughput can be maintained by having spare capacity to handle moves, breakdowns and refits.

-4-Berms left between cells may be mined later by truck and shovel or by dredge.
Completed cells are used for tailings and waste disposal. Discharge pipes from the dredges are floated in the ponds during the summer months, and carried by the ice during the winter.
As the oil sand and water are pumped out of the cell, an oil sand and water slurry is created and pumped via pipeline for further processing. Some initial separation of sand and oil particles occurs in the pipeline en route to the extraction plant.
In one embodiment of the process, the slurry is pumped to a floating treatment plant where excess water and cleaned sand are removed, and from there to an extraction plant via a pipeline downstream of the treatment plant. The excess water is returned to the pond, and cleaned sand is pumped to previously excavated cells.
In order to increase slurry temperature, hot water and conditioning agents may be added to the slurry at the treatment plant. Alternatively, warm tailings water may be piped directly to the cutter head, or a reduced-scale heating and mixing system may be installed on the barge. The warming of the slurry allows for sand and oil particle separation in the pipeline, and this effect is enhanced by increasing the distance of slurry travel from the pit itself all the way to the extraction plant.
An alternative process includes the location of a floating extraction plant on a barge.
The dredge includes sufficient space to allow for the addition of the required conditioning agents to the slurry. The pipeline from the dredge to the extraction plant may be much less than 2500 metres, provided that the extraction plant is of sufficient size to allow the enhanced settling out of sand to take place.
The floating extraction plant includes typical primary separation plant equipment, as well as means for separating the oil from the sand, and a bitumen frothing plant and pumping systems. These are all located on a floating barge which may be moved with little effort to the required location within the mine site. Since the extraction plant requires a uniform grade of oil sand to operate efficiently, multiple dredges may be required to process oil sands of varying bitumen content.
_5_ The bitumen froth is pumped directly from the floating extraction plant to an upgrader plant, while the cleaned sand effluent is pumped from the floating extraction plant to previously excavated areas within the mine site. Sludge from the upgrader plant is then pumped back to the primary separation plant where it is integrated with the pumped clean sand effluent.
The oil sands may be drilled or blasted, or sprayed with high-pressure water jets prior to excavation. This loosens the oil sands and reduces the difficulty of excavating hard ore zones.
The use of a dredge slurry and pipeline eliminates the need for an ore preparation plant and the hoppers, crusher-sizers, conveyors, and other equipment that are typically located in the ore preparation plant.
A distinct cost advantage of the process is the delivery of warm material during the winter. The ore being mined will be kept flooded with water, so that its temperature will never be lower than 0°C. This may make a difference of up to 30 or 40°C compared to current practices. There is a reduction in energy costs due to the higher average ore temperature.
The process also reduces the need for machinery used in excavating, hauling and crushing, and therefore requires far less energy than prior art processes.
Reduced need for equipment also results in lower C02 emissions - an important consideration in light of the Kyoto Protocol.
Further savings are realized through a lowering of ore cut-off grade. Since the cost of mining is significantly reduced with this method, it becomes cost-effective to mine a lower grade of ore. Accordingly, more of the lean oil sand may be classified as ore, thus enlarging the reserve and lowering the amount of stripping required.
Overall, significant cost reductions in the order of $2.00 per barrel are anticipated.
Brief Description of the Figures Figure 1 is a flow chart illustrating the traditional open-pit mining method (prior art).
Figure 2 is a flow chart illustrating a first embodiment of the flooded-pit dredge mining method.
Figure 3 is a flow chart illustrating a second embodiment of the flooded-pit dredge mining method.
Figure 4 is a flow chart illustrating the operating of the extraction plant.
Detailed Description of the Figures In Figure 1, the pit (1 ) is excavated with heavy-duty ground-engaging equipment (2).
Ore is transported by trucks (3) to a sizer (4) for breakage of large ore lumps. The ore is conveyed to a surge (5), and then is conveyed to a preparation plant (6) where it is mixed with water to form a slurry. The slurry is pumped to an extraction plant (7), where sand and bitumen are separated. Bitumen is pumped to an upgrader for processing, while sand and water are pumped to tailing ponds.
In Figure 2, the pit (1 ) is filled with water (8) and excavated with a dredge (9). The ore, along with some water, is conveyed directly to a preparation plant (6), where the cooler water may be replaced with hot water. The slurry is pumped to an extraction plant (7), where sand and bitumen are separated. Bitumen is pumped to an upgrader for processing, while sand and water are pumped to tailing ponds.
In Figure 3, the pit (1 ) is filled with water (8) and excavated with a dredge (9). A slurry is created by mixing the ore with water and conditioning agents on the dredge.
The slurry is then transported via pipeline (10) to an extraction plant (7) located on a floating barge (11 ). The bitumen is then pumped to an upgrader for processing, while sand and water are pumped to tailing ponds.

In Figure 4, the slurry arrives at the extraction plant (7) through a pipeline (10) from the dredge, and is first processed in a first separation circuit (12) to remove sand. Coarse tailings (13) including sand are removed and pumped to the tailings pond. The remaining froth is then further processed in a second separation circuit (14) to remove fine tailings (15) which are pumped to a tailings pond. The bitumen-containing froth (16) is then pumped to an upgrader for processing.
_g_

Claims (2)

I CLAIM:

1. A method for mining oil sand from an underground oil sand deposit comprising:

a) removing ground materials above said underground oil sand deposit to form a pit;

b) filling said pit with water;

c) removing said oil sand from said pit by means of a dredge at a site of extraction, and d) transporting said removed oil sand out from said pit for further processing.
wherein said removed oil sand is transported out from said pit to an extraction plant in the form of a slurry and said removed oil sand is processed in said extraction plant, said slurry being heated by warm tailing water pumped directly to the site of extraction, said extraction plant being located on a floating barge in the pit.

2. A method for mining oil sand as claimed in claim 1, wherein steps a) and b) are performed concurrently.